This invention relates generally to an assay for identifying the presence in a sample of an antibody which is immunologically reactive with a hepatitis C virus antigen and specifically to an assay for detecting a complex of an antibody and recombinant antigens representing distinct regions of the HCV genome. Recombinant antigens derived from the molecular cloning and expression in a heterologous expression system of the synthetic DNA sequences representing distinct antigenic regions of the HCV genome can be used as reagents for the detection of antibodies and antigen in body fluids from individuals exposed to hepatitis C virus (HCV).
Acute viral hepatitis is clinically diagnosed by a well-defined set of patient symptoms, including jaundice, hepatic tenderness, and an increase in the serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase. Additional serologic immunoassays are generally performed to diagnose the specific type of viral causative agent Historically, patients presenting clinical hepatitis symptoms and not otherwise infected by hepatitis A, hepatitis B, Epstein-Barr or cytomegalovirus were clinically diagnosed as having non-A non-B hepatitis (NANBH) by default. The disease may result in chronic liver damage.
Each of the well-known, immunologically characterized hepatitis-inducing viruses, hepatitis A virus (HAV), hepatitis B virus (HBV), and hepatitis D virus (HDV) belongs to a separate family of viruses and has a distinctive viral organization, protein structure, and mode of replication.
Attempts to identify the NANBH virus by virtue of genomic similarity to one of the known hepatitis viruses have failed, suggesting that NANBH has a distinct organization and structure. [Fowler, et al., J. Med. Virol., 12:205-213 (1983) and Weiner, et al., J. Med. Virol., 21:239-247 (1987)].
Progress in developing assays to detect antibodies specific for NANBH has been particularly hampered by difficulties in correctly identifying antigens associated with NANBH. See, for example, Wands, J., et al., U.S. Pat. No. 4,870,076, Wands, et al., Proc. Nat""l. Acad. Sci., 83:6608-6612 (1986), Ohori, et al., J. Med. Virol., 12:161-178 (1983), Bradley, et al., Proc. Nat""l. Acad. Sci., 84:6277-6281, (1987), Akatsuka, T., et al., J. Med. Virol, 20:43-56 (1986), Seto, B., et al., U.S. patent application Ser. No. 07/234,641 (available from U.S. Department of Commerce National Technical Information Service, Springfield, Va., No. 89138168), Takahashi, K., et al., European Patent Application No. 0 293 274, published Nov. 30, 1988, and Seelig, R., et al., in PCT Application PCT/EP88/00123.
Recently, another hepatitis-inducing virus has been unequivocally identified as hepatitis C virus (HCV) by Houghton, M., et al., European Patent Application publication number 0 318 216, May 31, 1989. Related papers describing this virus include Kuo, G., et al., Science, 244:359-361 (1989) and Choo, Q., et. al, Science, 244:362-364 (1989). Houghton, M., et al. reported isolating cDNA sequences from HCV which encode antigens which react immunologically with antibodies present in patients infected with NANBH, thus establishing that HCV is one of the viral agents causing NANBH. The cDNA sequences associated with HCV were isolated from a cDNA library prepared from the RNA obtained from pooled serum from a chimpanzee with chronic HCV infection. The cDNA library contained cDNA sequences of approximate mean size of about 200 base pairs. The cDNA library was screened for encoded epitopes expressed in clones that could bind to antibodies in sera from patients who had previously experienced NANBH.
In the European Patent Application, Houghton, M., et al. also described the preparation of several superoxide dismutase fusion polypeptides (SOD) and the use of these SOD fusion polypeptides to develop an HCV screening assay. The most complex SOD fusion polypeptide described in the European Patent Application, designated c100-3, was described as containing 154 amino acids of human SOD at the aminoterminus, 5 amino acid residues derived from the expression of a synthetic DNA adapter containing a restriction site, EcoRI, 363 amino acids derived from the expression of a cloned HCV cDNA fragment, and 5 carboxyl terminal amino acids derived from an MS2 cloning vector nucleotide sequence. The DNA sequence encoding this polypeptide was transformed into yeast cells using a plasmid. The transformed cells were cultured and expressed a 54,000 molecular weight polypeptide which was purified to about 80% purity by differential extraction.
Other SOD fusion polypeptides designated SOD-NANB5-1-1 and SOD-NANB81 were expressed in recombinant bacteria. The E.coli fusion polypeptides were purified by differential extraction and by chromatography using anion and cation exchange columns. The purification procedures were able to produce SOD-NANB5-1-1 as about 80% pure and SOD-NAN38, as about 50% pure.
The recombinant SOD fusion polypeptides described by Houghton, M., et al. were coated on microtiter wells or polystyrene beads and used to assay serum samples. Briefly, coated microtiter wells were incubated with a sample in a diluent. After incubation, the microtiter wells were washed and then developed using either a radioactively labelled sheep anti-human antibody or a mouse antihuman IgG-HRP (horseradish peroxidase) conjugate. These assays were used to detect both post acute phase and chronic phase HCV infection.
Due to the preparative methods, assay specificity required adding yeast or E.coli extracts to the samples in order to prevent undesired immunological reactions with any yeast or E. coli antibodies present in samples.
Ortho Diagnostic Systems Inc. have developed a immunoenzyme assay to detect antibodies to HCV antigens. The Ortho assay procedure is a three-stage test for serum/plasma carried out in a microwell coated with the recombinant yeast(hepatitis C virus SOD fusion polypeptide c100-3.
In the first stage, a test specimen is diluted directly in the test well and incubated for a specified length of time. If antibodies to HCV antigens are present in the specimen, antigen-antibody complexes will be formed on the microwell surface. If no antibodies are present, complexes will not be formed and the unbound serum or plasma proteins will be removed in a washing step.
In the second stage, anti-human IgG murine monoclonal antibody horseradish peroxidase conjugate is added to the microwell. The conjugate binds specifically to the antibody portion of the antigen-antibody complexes. If antigen-antibody complexes are not present, the unbound conjugate will also be removed by a washing step.
In the third stage, an enzyme detection system composed of o-phenylenediamine 2HCl (OPD) and hydrogen peroxide is added to the test well. If bound conjugate is present, the OPD will be oxidized, resulting in a colored end product. After formation of the colored end product, dilute sulfuric acid is added to the microwell to stop the color-forming detection reaction.
The intensity of the colored end product is measured with a microwell reader. The assay may be used to screen patient serum and plasma.
It is established that HCV may be transmitted by contaminated blood and blood products. In transfused patients, as many as 10% will suffer from post-transfusion hepatitis. Of these, approximately 90% are the result of infections diagnosed as HCV. The prevention of transmission of HCV by blood and blood products requires reliable, sensitive and specific diagnosis and prognostic tools to identify HCV carriers as well as contaminated blood and blood products. Thus, there exists a need for an HCV assay which uses reliable and efficient reagents and methods to accurately detect the presence of HCV antibodies in samples.
The present invention provides an improved assay for detecting the presence of an antibody to an HCV antigen in a sample by contacting the sample with at least one recombinant protein representing a distinct antigenic region of the HCV genome. The recombinant antigens include .SEQ. ID. NO 2, SEQ. ID. NO 4, SEQ. ID. NO 6, SEQ. ID. NO 8, SEQ. ID. NO 10, SEQ. ID. NO 12, SEQ. ID. NO 14, SEQ. ID. NO 16, SEQ. ID. NO 18, SEQ. ID. NO 20, SEQ. ID. NO 22, SEQ. ID. NO 24, SEQ. ID. NO 26, SEQ. ID. NO 28, SEQ. ID. NO 30, SEQ. ID. NO 58, SEQ. ID. NO 59, SEQ. ID. NO. 31, SEQ. ID. NO. 32, SEQ. ID. NO. 33, SEQ. ID. NO. 34, SEQ. ID. NO. 35, SEQ. ID. NO. 36, SEQ. ID. NO 47, SEQ. ID. NO. 48, SEQ. ID. NO. 49, SEQ. ID. NO. 50, SEQ. ID. NO. 52, SEQ. ID. NO. 53 and SEQ. ID. NO. 54.
One assay format according to the invention provides a screening assay for identifying the presence of an antibody that is immunologically reactive with an HCV antigen. Briefly, a fluid sample is incubated with a solid support containing the two commonly bound recombinant proteins HCV pHCV-34 (SEQ. ID. NO. 2) and pHCV-31 (SEQ. ID. NO. 4). Finally, the antibody-antigen complex is detected. In a modification of the screening assay the solid support additionally contains recombinant polypeptide c100-3.
Another assay format provides a confirmatory assay for unequivocally identifying the presence of an antibody that is immunologically reactive with an HCV antigen. The confirmatory assay includes synthetic peptides or recombinant antigens representing major epitopes contained within the three distinct regions of the HCV genome, which are the same regions represented by the two recombinant proteins described in the screening assay. These regions include NS4 (the c100-3 region) represented by pHCV-23 (SEQ. ID. NO 58), NS3 (the 33c region) represented by pHCV-29 (SEQ. ID. NO. 59), and together with pHCV-23 (the c100-3 region) represented by pHCV-31, and a region near the 5xe2x80x2 end of the HCV genome believed to be the core structural protein of HCV (pHCV-34). Recombinant proteins used in the confirmatory assay should have a heterologous source of antigen to that used in the primary screening assay (i.e. should not be an E.coli-derived recombinant antigen nor a recombinant antigen composed in part, of CKS sequences). Briefly, specimens repeatedly reactive in the primary screening assay are retested in the confirmatory assay. Aliquots containing identical amounts of specimen are contacted with a synthetic peptide or recombinant antigen individually coated onto a solid support. Finally, the antibody-antigen complex is detected. Seroreactivity for epitopes within the c100-3 region of the HCV genome are confirmed by use of the synthetic peptides sp67 and sp65. The synthetic peptide sp117 can also be used to confirm seroreactivity within the c100-3 region. Seroreactivity for HCV epitopes within the putative core region of HCV are confirmed by the use of the synthetic peptide sp75. In order to confirm seroreactivity for HCV epitopes within the 33c region of HCV, a recombinant antigen is expressed as a chimeric protein with superoxide dismutase (SOD) in yeast. The synthetic peptide sp65 (representing amino acids p1866-1930 of the HCV sequence), sp67 (representing amino acids p1684-1750), sp75 (representing amino acids p1-75), and sp117 (representing amino acids p1689-1805) are described in U.S. Ser. No. 456,162 entitled xe2x80x9cHepatitis C Assayxe2x80x9d, filed Dec. 22, 1989, which enjoys common ownership and is incorporated herein by reference.
Another assay format provides a competition assay or neutralization assay directed to the confirmation that positive results are not false by identifying the presence of an antibody that is immunologically reactive with an HCV antigen in a fluid sample where the sample is used to prepare first and second immunologically equivalent aliquots. The first aliquot is contacted with solid support containing a bound polypeptide which contains at least one epitope of an HCV antigen under conditions suitable for complexing with the antibody to form a detectable antibody-polypeptide complex and the second aliquot is first contacted with the same solid support containing bound polypeptide. The preferred recombinant polypeptide is derived from pHCV-23.
Another assay format provides an immunodot assay for identifying the presence of an antibody that is immunologically reactive with an HCV antigen by concurrently contacting a sample with recombinant polypeptides each containing distinct epitopes of an HCV antigen under conditions suitable for complexing the antibody with at least one of the polypeptides and detecting the antibody polypeptide complex by reacting the complex with color producing reagents. The preferred recombinant polypeptides employed include those recombinant polypeptides derived from pHCV-23, pHCV-29, pHCV-31, pHCV-34, as well as c100-3 expressed as a chimeric protein with superoxide dismutase (SOD) in yeast.
In all of the assays, the sample is preferably diluted before contacting the polypeptide absorbed on a solid support. Samples may be obtained from different biological samples such as whole blood, serum, plasma, cerebral spinal fluid, and lymphocyte or cell culture supernatants. Solid support materials may include cellulose materials, such as paper and nitrocellulose, natural and synthetic polymeric materials, such as polyacrylamide, polystyrene, and cotton, porous gels such as silica gel, agarose, dextran and gelatin, and inorganic materials such as deactivated alumina, magnesium sulfate and glass. Suitable solid support materials may be used in assays in a variety of well known physical configurations, including microtiter wells, test tubes, beads, strips, membranes, and microparticles. A preferred solid support for a non-immunodot assay is a polystyrene bead. A preferred solid support for an immunodot assay is nitrocellulose.
Suitable methods and reagents for detecting an antibody-antigen complex in an assay of the present invention are commercially available or known in the relevant art. Representative methods may employ detection reagents such as enzymatic, radioisotopic, fluorescent, luminescent, or chemiluminescent reagents. These reagents may be used to prepare hapten-labelled antihapten detection systems according to known procedures, for example, a biotin-labelled antibiotin system may be used to detect an antibody-antigen complex.
Polypeptides also are provided. These include SEQ. ID. NO 2, SEQ. ID. NO 4, SEQ. ID. NO 6, SEQ. ID. NO 8, SEQ. ID. NO 10, SEQ. ID. NO 12, SEQ. ID. NO 14, SEQ. ID. NO 16, SEQ. ID. NO 18, SEQ. ID. NO 20, SEQ. ID. NO 22, SEQ. ID. NO 24, SEQ. ID. NO 26, SEQ. ID. NO 28, SEQ. ID. NO 30, SEQ. ID. NO 58, SEQ. ID. NO 59, SEQ. ID. NO. 31, SEQ. ID. NO. 32, SEQ. ID. NO. 33, SEQ. ID. NO. 34, SEQ. ID. NO. 35, SEQ. ID. NO. 36, SEQ. ID. NO 47, SEQ. ID. NO. 48, SEQ. ID. NO. 49, SEQ. ID. NO. 50, SEQ. ID. NO. 52, SEQ. ID. NO. 53 and SEQ. ID. NO. 54.
The present invention in addition provides plasmids. These plasmids include those with the following sequences: SEQ. ID. NO. 58, SEQ. ID. NO. 59, SEQ. ID. NO.4 and SEQ. ID. NO. 2.
The present invention also encompasses assay kits including containers containing polypeptides or recombinant proteins which contain at least one epitope of an HCV antigen bound to a solid support as well as a containers containing needed sample preparation reagents, wash reagents, detection reagents and signal producing reagents.
Other aspects and advantages of the invention will be apparent to those skilled in the art upon consideration of the following detailed description which provides illustrations of the invention in its presently preferred embodiments.
E.coli strains containing plasmids useful for constructs of the invention were deposited at the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Md. on Aug. 10, 1990, under the accession Nos. ATCC 68380 (pHCV-23), ATCC 68381 (pHCV-29), ATCC 68382 (pHCV-31), ATCC 68383 (pHCV-34, and on Nov. 6, 1990 for E.coli strains containing plasmids useful for constructs under the accession Nos. ATCC 68458 (pHCV-50), ATCC 68459 (pHCV-57), ATCC 68460 (pHCV-103), ATCC 68461 (pHCV-102), ATCC 68462 (pHCV-51), ATCC 68463 (pHCV-105), ATCC 68464 (pHCV-107), ATCC 68465 (pHCV-104), ATCC 68466 (pHCV-45), ATCC 68467 (pHCV-48),ATCC 68468 (pHCV-49), ATCC 68469 (pHCV-58) and ATCC 68470 (pHCV-101). E. coli strains containing plasmids useful for constructs of the invention also were deposited at the A.T.C.C. on Sep. 26, 1991 under deposit numbers ATCC 68690 (pHCV-77), ATCC 68696 (pHCV-65), ATCC 68689 (pHCV-78), ATCC 68688 (pHCV-80) and ATCC 68695 (pHCV-92), ATCC 68691 (pHCV-59), ATCC 68692 (pHCV-62), ATCC 68687 (pHCV-63), ATCC 68685 (pHCV-72), ATCC 68684 (pHCV-73), ATCC 68694 (pHCV-204), ATCC 68693 (pHCV-205) and ATCC 68686 (pHCV-112).